Such a hydraulic machine is known for example from U.S. Pat. No. 3,915,603. The gear wheel rotates and orbits during operation. Between the rollers and the gear wheel the pressurized spaces are formed, of which spaces about one half are filled with hydraulic fluid under high pressure and the remaining half are filled with hydraulic fluid under lower pressure. The engagement between the rollers and the gear wheel must especially provide sealing at two positions; namely, at the two points of separation between a high-pressure space and an adjacent low-pressure space.
At one of these points of separation, the boundary between the high-pressure and low-pressure spaces is formed by one roller together with the peak of a tooth of the gear wheel. This roller is subjected to an especially high loading. This roller is not only pressed into its pocket by the gear wheel, but also the pressure of the high-pressure space acts on the roller to, so to speak, “urge” the roller out of its pocket in the circumferential direction. In this situation, the engagement surface area between the roller and the pocket is diminished so that a higher pressure is exerted on the roller. This higher pressure is especially detrimental if the roller is engaging practically only on the edge of its pocket, where the pocket transitions to the inner surface of the gear ring in the circumferential direction. Under unfavorable conditions this can lead to the edge making a permanent impression in the roller. Then this impressed roller tends to stand still while all the other loaded rollers rotate in normal fashion. If the roller stands still then no rolling contact occurs between the gear wheel and the roller, and the wear of these components is disproportionately large. Even without the formation of such an impression, in most cases a considerable wear, either of the edge of the pocket or of the roller, still results. This wear impairs the sealing ability of the machine and accordingly the machine's efficiency and useful life.
The above mentioned U.S. Pat. No. 3,915,603 has tried to solve this problem by forming the pocket with a larger radius than the roller, so that the roller in certain situations can yield to the pressure from the higher-pressure space. This however, leads to the fact that the point of separation between the high-pressure space and the low-pressure space is not absolutely sealed, which can lead to internal leakage. To avoid this leakage, expensive measures securing the pressure delivery to the pocket are required.
Also in U.S. Pat. No. 3,930,766, the pockets have been formed with larger radii than the rollers, which again brings with it sealing problems.
U.S. Pat. No. 4,008,015 shows a construction in which the pockets again have a larger radii than the ball. To accommodate the radii-difference the pocket is lined with a filling formed by a porous material. This porous material can absorb hydraulic fluid and thereby offer an improved lubrication.